The present invention relates to an apparatus for measuring metal loss in industrial process and downhole environments. In particular, the present invention relates to a probe which permits direct measurement of electrical resistance which can provide an estimation of the metal loss at the surface of industrial or process equipment.
In industrial and process environments the corrosion of pipes and vessels poses a major concern. System failure due to corrosion can result in extensive downtime, can result in widespread systemic damage or failure, and can endanger the health and safety of individuals operating the system. Therefore it is beneficial to accurately monitor corrosion and degradation rates to facilitate the replacement or repair of weakened pipes or vessels before structural failure is experienced.
Probes that assess corrosion levels by measuring electrical resistance are well known. Commonly, the probe is comprised of a metal element that is subjected to the corrosive environment inside the pipe or vessel. The element is made from the same material as the pipe or vessel and because it is being subjected to the same environment as the pipe or vessel, corrosion levels on the metal element can be correlated to corrosion levels on the pipe or vessel. The level of corrosion on the metal element is monitored by assessing its electrical resistance and comparing it to the resistance of a reference element, insulated from the corrosive environment. The measurements involve a ratio-metric comparison of the resistivity of the reference element and the exposed element. The metal elements may project into the pipe or vessel, or alternatively they can be inserted such that they are flush with the pipe of vessel wall thereby facilitating the contemporaneous use of cleaning and monitoring equipment pigs.
There are a number of problems associated with the existing probes. The use of ratiometric measurement to compare a corroding element with a reference element is limited in accuracy and resolution. Current probes do not integrate electronics and memory and rely on transmitting readings to an external analysis and storage system by means of cables or wires. The remote nature of the electronics and memory components results in undesired effects that reduce the precision of the readings obtained from the exposed metal element. The remote electronics and memory components increase the complexity and cost of the corrosion detection system and can often be impractical to utilize in the industrial or field setting. Further, with existing probes, integral temperature compensation must be conducted which increases the complexity of accurate data interpretation. This problem is amplified by the introduction of additional thermal effects due to the manufacturing processes utilized. Also the data obtained from current probes is often difficult to read and interpret or reproduce.
Therefore, there is a need in the art for a direct resistance measurement corrosion probe that overcomes the existing limitations of the prior art.